| 摘要 |
<p>A tri-element carbon based heat shield has an outer layer including a carbon-carbon composite, a middle layer including pyrolytic graphite deposited onto an inner surface of the outer layer and an inner layer including carbon felt or foam having low density and high mechanical compliance. The thickness of each layer is selected for optimizing thermal protection over the expected operating temperature range. Although a carbon-carbon composite has a higher thermal diffusivity (inversely related to thermal insulation efficiency) than pyrolytic graphite, the carbon-carbon is selected as the outer layer in a minimum thickness sufficient to satisfy the structural strength, ablation and recession requirements of the heat shield. The resulting thickness of the outer layer determines the operating temperature range of the middle layer. At a predetermined temperature, the thermal diffusivity of the inner layer becomes less than that of the middle layer so that the thickness of the inner layer is selected to operate from this predetermined temperature to all lower temperatures.</p> |
